One of the biggest drivers for selection of a terminal block is the centerline that is going to be required. Centerline spacing is generally dictated by the amount of current that will be handled, but other factors such as the screw head size may also come into play. The bottom three bullets show some other configuration or design options available. Terminal blocks are often times marked or printed on for circuit identification purposes. Different colors such as green, black, grey, blue, red, or yellow are occasionally used for identification or general aesthetic purposes. High temperature terminal blocks may also be required for special through-hole reflow soldering processes.